Controllable inductors and methods of assembly



July 22, 1958 E. A. FAvREAu, JR., ETAL CONTROLLABLE INDUCTORS AND METHODS OF ASSEMBLY Filed Aug. $1, 1956 JNVEIVTORS. ELIE ARTHUR FAVREAQR BYHERBERT ROSHKQND United States Patent CONTROLLABLE INDUCTORS AND METHODS OF ASSEMBLY Elie Arthur Favreau, Jr., Stamford, and Herbert Roshkind, Westport, Conn., assignors to C. G. S. Laboratories, Inc., Stamford, Conn., a corporation of Connecticut Application August 31, 1956, Serial No. 607,492

15 Claims. (Cl. 336-455) The present invention is in the field of improved controllable inductors and methods of assembly. More particularly this invention relates to improved controllable inductors of the type having a control magnetic yoke structure including at least two spaced legs with a plurality of magnetically saturable elements spanned across between them.

In the illustrative embodiment of the invention described herein, these magnetically saturable elements are in the form of rods secured in place spanning across be tween the legs of the control yoke structure. Wound on these rods are signal windings whose inductance is being controlled. A control winding associated with the control yoke structure acts to vary the degree of magnetic saturation of these saturable elements. This regulates their eifective permeability and thus controls the efiective or incremental inductance of the signal windings wound thereon.

Among the many advantages of this controllable inductor are those resulting from the fact that spring retaining clips hold the saturable rod elements securely in place upon the control yoke structure. These clips accurately predetermine the spacing of the saturable rods. In addition, the clips provide shielding effective for directing the alternating magnetic fields associated with the signal windings into desired paths for extended ranges of operation and more efficient control action.

Advantageously, during assembly the saturable rods can be quickly and easily positioned with respect to the yoke structure and are readily snapped into place in the retaining clips. Tapered notches in the clips hold the rods firmly and press them securely into engagement with the legs of the yoke structure, thus providing a good magnetic circuit.

An advantage of the retaining clips as shown is that they firmly hold one rod spanned across the extreme ends of the legs of the yoke structure while at the same time holding one or more saturable elements against the sides of these legs. An accurately predetermined spacing is maintained between all of the rods as desired for optimum operation.

Another advantage of the spring clips as shown and described herein results from the fact that they are formed of metal having relatively high electrical conductivity. These provide desirable shielding between the high-frequency magnetic flux associated with the signal windings and the legs of the yoke structure. In this way, the Signal flux is forced to conform more closely to the lengths of the rods and to return through the air along the most efficient paths.

Among the further advantages of this improved controllable inductor are its rugged ability to resist misalignment of the saturable rods and to retain its enhanced operating characteristics in spite of rough usage.

The improved controllable inductor described herein is in the nature of a further improvement over the inductor described in detail and claimed in the copending ap- 2 plication of William D. Gabor, Serial No. 457,265, filed September 24, 1954. I

In this specification and in the accompanying drawings, is described and shown an illustrative embodiment of our improved controllable inductor and various modifications thereof are suggested, but it is to be understood that these are not intended to be exhaustive nor limiting of the invention, but on the contrary are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the manner of applying the method and apparatus in practical use so that they may modify and adapt it in various forms, each as may be best suited to the conditions of a particular use.

The various features, aspects, and advantages of our invention will be more fully understood from a consideration of the following specification in conjunction with the accompanying sheet of drawings, in which:

Figure 1 is a perspective view of an improved controllable inductor embodying the present invention and illustrating the spring retaining clips in position holding the three saturable rod elements spanned across between the legs of the control yoke structure;

Figure 2 is a top view as seen looking down toward the upper ends of the legs of the yoke structure in Figure 1;

Figure 3 is a cross sectional view taken along the line 33 in Figure 1 looking toward the left; and

Figure 4 is a perspective view on enlarged scale of one of the spring retaining clips for securing the saturable rod elements in place.

The improved controllable inductor shown in Figures 1, 2, and 3 includes a U-shaped yoke structure, generally indicated at 10 and including a back portion 12 forming the bottom of the U-shape. A pair of legs 14 and 16 are upstanding from opposite ends of the back portion 12. As indicated in the cross sectional view in Figure 3, this yoke structure is formed from stacked U-shaped laminations. The legs 14 and 16 have approximately a square cross section.

In order to control the operation of this controllable inductor, a control winding is associated with the yoke structure 10. As shown, this includes a pair of wind ings 18 and 20 wound on cylindrical bobbins 22 and 24 having an internal clearance opening just large enough to slide over the legs 14 and 16, respectively. These bobbins are slid down until they abut against the back 12 of the yoke structure. They leave a substantial length of the legs 14 and 1.6 projecting up beyond the ends of the respective bobbins. As shown, the projecting length of the leg is approximately equal to the length of the bobbin. The two windings 18 and 20 are connected in series aiding relationship to form a single control winding.

During assembly, as soon as the bobbins 22 and 24 are slid down over the legs 14 and 16 into place, a left and a right spring retaining clip 26 and 28, respectively, are assembled with the bobbins and yoke structure. These retaining clips each have a body of L-shaped cross section with one face 29 adapted to lie against the inside surfaces of the legs 14 and 16 and another face 30 adapted to extend across behind these legs. Each clip includes a downwardly projecting blade 31 (seen most clearly in Figure 4). A short lower end portion 32 of the blade is bent inwardly with respect to the faces 29 and 30.

In order to fit snugly down through the interior of the bobbins 22 and 24, the blade portions 31 and 32 ofthese retaining clips are slightly narrower than the thickness of the legs 14 and 16. They have a total length slightly greater than the axial length of the opening through the bobbins.

In the next step of the assembly, these blades of the two retaining clips are slid down within the respective openings of the bobbins. The bent portions 32 at the lower end of these blades resiliently bind the blades within the bobbins and desirably hold the faces 29 and 30 firmly against the inside and back surfaces of the yoke legs, respectively. A plurality of saturable rod elements 35, 36, and 37 are secured in place spanned across between the legs 14 and 16 by means of these clips 26 and 28.

The first one of the saturable rod elements 35 has a larger diameter and extends across at the ends of the legs 14 and 16. A pair of accurately spaced saturable rod elements 36 and 37 of smaller diameter and greater length than rod 35 extend across the width of the yoke structure in position firmly against the side surfaces of the legs 14 and 16.

The laminations comprising the control yoke structure are of transformer iron having a relatively high permeability and capable of carrying a high flux density. The saturable rod elements 35, 36 and 37 are characterized by a high initial permeability and a low saturation flux density. Their effective or incremental permeability decreases rapidly with increase in the degree of saturation provided by the control fiux supplied from the yoke structure. In this embodiment these saturable elements are cylindrical rods of ferromagnetic ceramic, also called ferrite.

In order to secure the ends of the rod 35 firmly in place on the ends of the yoke legs, the retaining clips both include an upper or forefinger 40 (as seen most clearly in Figure 4). This finger 40 is positioned above the upper outer corner of the body portion 29 and provides an edge 42 coacting with a thumb 44 above the back face 30 to hold the rod 35.

Between the thumb 44 and the edge 42 is defined a trapezoidal-shaped opening 46 into which is fitted the end of the rod 35. In effect, the thumb 44 and finger 40, in grasping and holding a rod firmly in place, co-operate in a manner similar to the action of the thumb and forefinger of a hand. The finger 40 is bent inwardly with respect to the plane of the body portion 29.

As shown most clearly in Figure 3, this upper finger 40 is positioned away from the corner 34 of the clip a distance approximately equal to the thickness of the yoke legs so that when the clip is in assembled relationship with its respective yoke leg, the rod-retaining edge 42 is approximately in line with the front surface of the respective yoke leg.

The thumb 44 projects up from the upper end of the back face 30 of the retaining clip. This thumb 44 is bent inwardly with respect to the plane of the back face 30, while the edge 42 is straight and lies in a plane parallel with the corner 34. As most clearly illustrated in Figure 3, when the rod 35 is pressed into the opening 46 the thumb 44, by its inward inclination, resiliently presses the rod forwardly against the edge 42 and down toward the end of the yoke leg. In co-operation with this pressure, the straight edge 42 guides the rod 35 squarely into the desired accurately aligned position across the ends of the yoke legs. Thus, advantageously, the rod 35 is held firmly against the ends of the core legs and is precisely positioned with respect to the plane of the front face of the yoke legs 14 and 16. By virtue of its inward bend, the edge 42 of the finger 40 lies ahead of the thumb 44 in the position for effectively grasping and aligning the rod 35.

The saturablerod element 35 is shorter than the other two rods 36 and 37 and is adapted for operation over a wide band at a range of high frequencies of the order of a hundred megacycles. For preventing the alternating signal flux in the rod 35 from entering the yoke laminations, thin cap shims 56 of electrically conductive foil such as aluminum, fit between the ends of the legs 14 and 16 and the adjacent surfaces of the saturable rod element 35.

To hold the saturable elements 36 and 37 in place, the

body portion 29 also includes three lateral fingers defining therebetween a pair of trapezoidal-shaped openings 46 and 48. A narrow slot 50 continues back from the lower corner of the opening 48 across the body portion 29 to the corner 34. A similar slot 54 extends back from the opening 52 to the corner 34. These slots advantageously provide an increased resiliency for grasping the rods 36 and 37 in the openings 48 and 52 and' facilitate the assembling of these rods into the clips.

For accurately positioning and aligning the rods 36 and 37, the lower edges of the openings 48 and 52 are straight and extend out perpendicular to the corner 34. When assembled onto a yoke leg, the body portion 29 extends out beyond the side of the yoke leg, positioning the openings 48 and 52 to receive and hold the rods. Advantageously, the tapering upper edges of these notches holds the rods 36 and 37 firmly down against the straight lower edges while continuously urging them back tightly against the front faces of the yoke legs, as desired.

To insure that the rods 36 and 37 seat firmly against the front surfaces of the yoke legs, the distance between the corner 34 and the back edges of the openings 48 and 52 is less than the thickness of the yoke legs.

A further advantage of these retaining clips is that each of the three rod-retaining openings is trapezoidalshaped. Thus, each opening has one straight side which is perpendicular to the surface of the yoke leg against which the corresponding rod element is seated. This perpendicular edge provides an aligning abutment which will accurately and positively position the respective rod in place and maintain the desired spacing between rods, regardlessof dimensional variations during manufacture of the rods. A component of force toward this abutment and a component of force toward the seating surface on the yoke leg is provided by the inclined edge of the opening opposite to this abutment.

It is dilficult during manufacture of the ferrite saturable rod elements to prevent dimensional variations in rod diameter from occurring in different batches of the rods. The ferromagnetic ceramic material in the rods is too hard for conventional machining operations. Consequently, variations in rod diameters are present periodically during assembly. Nevertheless, the effective desirable grasping action of these trapezoidal-shaped openings automatically compensates for rod diameter variations. As a result, all of the rods are properly spaced apart and aligned during assembly as soon as they are snapped into place in the retaining clips.

The signal windings whose inductance is to be controlled are located near the respective centers of these rods 35, 36 and 37. For example, as shown, the rod 37 includes a forty-two-turn winding 74 around its center portion. Rod 36 includes a pair of windings 70 and 72, the former having four turns and the other having eleven turns. The rod 35 includes'a single-turn winding formed by a pair of conductive straps 58 and 60, passing over and under the rod, respectively. Their front corners are closely adjacent each other and are coupled together in a circuit as explained in detail in the aboveidentified application, effectively forming a single-tum winding at the highest operating frequencies. These straps diverge toward the rear side of the inductor into spaced relationship suitable for securing to terminal posts of a condenser, as explained in detail in the above copending application. The width of these straps 58 and 60 reduces theirself-inductance as is desirable at the highest frequencies of operation.

In the higher frequency portions of its operating range, there is a tendency for the magnetic flux associated with the single turn winding 5860 to divert from the desired path. This desired path lies parallel to the axis of the rod element 35, as the flux passes through between the straps 58 and60. 'To aid in guiding this flux along the desired path, the upper conductive strap 58 is formed with a relatively great width, hereshown as being approximately one-half its average length. 'In addition, a lateral wing 62 projects from one edge of this strap and lies along the top surface of the rod 35 parallel with its axis. Another lateral wing 64 is shown projecting from the opposite side of the strap 58.

These lateral wings also are advantageous in securing the strap 58 in place and at the proper angle with respect to the axis of the rod 35.

In order to control the effective magnetic length of the rod 35, a short-circuited loop of conductive wire 66 surrounds the rod at a position spaced about one-third of its length from the left end. A small strip of insulation tape 68 overlies this shorted loop underneath the conductive wing 62.

It will be noted that with the conductive retaining clips 26 and 28 in place, the inside surfaces and the rear surfaces of the yoke legs 14 and 16 are effectively shielded with layers of conductive material. The cap shims 56 shield the end of these legs. In addition, the rod elements are all precisely aligned in the desired positions regardless of any dimensional variations which may be present. These rods are positively secured in place in firm engagement with the yoke legs. This improved controllable inductor is easier to assemble and provides improved efficiency in control action. I

After final assembly as shown in Figures 1-3, the controllable inductor is, for many applications, coated with a protective layer of insulating plastic material.

From the foregoing it will be understood that the improved controllable inductor of the present invention described above is well suited to provide the advantages set forth, and since many possible embodiments may be made of the various features of this controllable inductor and as the apparatus herein described may be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense and that in certain instances, some of the features of the invention may be used without a corresponding use of other features, or without departing from the scope of the invention.

We claim:

1. An improved controllable inductor including a yoke structure having a pair of leg portions projecting therefrom, a saturable element having a generally rod-like configuration and being spanned across between the leg portions of said yoke structure, a retaining clip adjacent a surface of each of said leg portions, each retaining clip including fingers projecting beyond the edge of the respective adjacent surface and defining a rodretaining space therebetween, said saturable element fitting into the respective spaces between the fingers of said clips and being retained by said fingers pressed firmly toward the adjacent surface of said leg portions of the yoke structure.

2. An improved controllable inductor including a yoke structure having a pair of legs projecting therefrom, a rod-like magnetically saturable element spanned across between said yoke legs and at least partially overlapping the yoke legs on each side, a pair of retaining clips, one of said clips being associated with each of said yoke legs and resting adjacent the respective inside surfaces of said yoke legs, said retaining clips being substantially parallel with each other and both having an edge portion projecting beyond the respective limits of the inside surfaces of said yoke legs, said projecting edge portions defining at least one rod-retaining notch therein, and said rod-like element fitting into said notches and being retained by said clips firmly against said yoke legs.

3. An improved controllable inductor having a generally U-shaped control yoke structure with a pair of upstanding legs projecting from a back portion of said yoke structure, a plurality of saturable rod-like elements spanned between said legs, a pair of control winding portions wound around each of said legs, a pair of retaining clips each having a generally L-shaped cross sectional configuration with a first face adapted to rest against a side surface of one of said legs and a second face adapted to rest against the back surface of one of said legs, each clip having a blade portion projecting downwardly therefrom adapted to slide within one of said windings, said blade portion being deformed out of its own plane, thereby resiliently binding within the winding so as to hold the clip firmly against the leg, an edge of said first face of each clip having at least two openings therein, each of said openings including tapered rod-gripping means, one of said rod-like elements being fitted into each of said openings, said tapered means resiliently urging the respective element into the associated opening, an upper finger projecting upwardly from said first face and being bent inwardly, a thumb extending up from said second face and being bent inwardly, said upper finger and thumb coacting to hold one of said elements firmly adjacent to the ends of said legs.

4. An improved controllable inductor including a mag-- netic yoke structure having a pair of spaced legs, con trol winding means associated with said yoke structure and arranged to control the magnetic flux in said legs, a magnetizable rod-like element spanned across between said legs, and a retaining clip at least partially embracing and shielding each of said legs and having a blade portion extending within said control Winding means and having means defining a resilient opening in the retaining clip, said rod-like element being held by the opening in said clip in position spanned across between said legs.

5. An improved controllable inductor including a magnetic yoke structure having a pair of legs projecting therefrom, and electromagnetic means controlling the magnetic flux in said legs, a magnetically saturable rodlike element spanned across between the legs of said yoke structure, and retaining clip means having edge portions projecting beyond corresponding surfaces of each of said legs, said edge portions having trapezoidal-shaped openings therein holding opposite ends of said element and including abutment means perpendicular to the respective adjacent surface of one of the yoke legs and inclined means gripping said element and pressing it against the abutment means and against the respective adjacent surface of one of the yoke legs.

6. An improved controllable inductor including a yoke structure having a pair of legs of rectangular cross section projecting therefrom, a magnetically saturable rodlike element spanned across between the legs of said yoke structure, a pair of retaining clips each having an L-shaped cross-sectional configuration including a corner, a rear face extending out from the corner and lying against a rear surface of a respective one of said legs and a side face extending out from the corner and lying against a side surface of the respective leg, an edge of each side face projecting beyond the limit of the ad jacent side surface of the respective leg, said edge having a tapered notch therein enlarging toward said corner of the clip and gripping one end of said rod-like element therein and securing said saturable element against the sides of said leg portions.

7. An improved controllable inductor as claimed in claim 6 wherein said side face of each clip includes a slot therein extending back from said notch a substantial portion of the distance to said corner.

8. An improved controllable inductor including a yoke structure having a pair of legs projecting therefrom, electromagnetic control means associated with said yoke structure for controlling the magnetic flux in said legs, a rod-like magnetically saturable element spanned across between the ends of said legs and at least partially overlapping the ends of the legs at each end, a pair of retaining clips, one of said clips being associated with each of said legs, each of said clips having an L-shaped configuration and including a corner running parallel with the axis of the respective associated leg and a pair of faces extending outwardly from said corner, said faces lying against two surfaces of the respective leg, a thumb element projecting from one of said faces beyond the end of the respective leg and being inclined inwardly and a finger element projecting from the other of said faces beyond the end of the respective leg, said thumb and finger of each clip holding one end of said rod-like element firmly against the end of each one of said legs.

9. An improved controllable inductor as claimed in claim 8 and wherein said thumb and finger define a trapezoidal-shaped opening therebetween at the end of the respective leg as seen in a direction axially of said rodlike element.

10. An improved controllable inductor as claimed in claim 8 and wherein said finger element is also inclined inwardly into a position opposite said thumb, whereby said thumb and finger element grasp an end of said rodlike element effectively from opposed positions.

11. An improved controllable inductor having a generally U-shaped control yoke structure with a pair of up standing legs of rectangular cross section projecting from a back portion of said yoke structure, a pair of control winding portions around each of said legs, a pair of retaining clips each associated with one of said legs and each having a generally L-shaped cross sectional configuration with a corner lying along a corner of a respective one of said legs and a first face resting against the inside surface of the respective leg and with a second face resting against the back surface of the respective leg, said first face of the clip having a blade portion projecting downwardly therefrom and fitting within the respective one of said windings, said blade portion resiliently binding within the winding so as to hold the clip firmly in position, the edge of said first face projecting beyond the front surface of the respective leg and having at least one trapezoidal-shaped notch therein, a finger element projecting above said first face and a thumb projecting above said second face, both said finger and thumb element extending beyond the respective end of the leg, and a plurality of rod-like saturable members extending across between said legs, one of said rod-like members fitting into said notches and being held thereby and one of said members being held adjacent the respective ends of said legs by said finger and thumb element.

12. An improved controllable inductor as claimed in claim 11 and wherein each of said projecting edges includes a plurality of trapezoidal-shaped openings therein and each of the first faces of the clips include slots extending back from the opening to the corner of said clip.

13. An improved controllable inductor as claimed in claim 12 wherein one limit of each opening is perpendicular to the corner of the clip and the slot extends back as a continuation of said limit.

14. A controllable inductor having a plurality of signal windings and control winding means for controlling the effective inductance of the signal windings including a magnetic yoke portion having a pair of projecting legs, control winding means on said yoke portion, a plurality of rods of magnetically saturable material extending across between the legs of the magnetic yoke portion, a signal winding coupled to each of said rods, the ends of the rods being in overlapping relationship with said legs, and a pair of retainers for holding said rods in spaced parallel relationship, said retainers each including a body portion extending along beside each of said legs with fingers extending out beyond the overlapped portion of said legs, said fingers passing between the ends of said rods for maintaining said rods in their spaced parallel alignment extending across between the legs of said yoke portion.

15. A controllable inductor having a plurality of signal windings and a control winding for controlling the effective inductance of the signal windings, said controllable inductor including a U-shaped magnetic yoke structure having a pair of legs, a control winding divided into two portions, each portion being wound around a respective one'of said legs, a plurality of rods of magnetically saturable material extending across between said legs, said rods being in spaced parallel relationship with the end portions of said rods being in overlapping relationship with said legs, a signal winding on each of said rods, and a pair of retainers for said rods, each of said retainers being adjacent to a respective one of said legs and having a projecting part fitting along the leg into the winding, each of said retainers having a plurality of fingers projecting beyond the respective adjacent leg and between the end portions of the rods for holding the rods in spaced parallel relationship extending across between the legs of the yoke structure.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,123 Ballantine July 4, 1939 2,462,423 Polydoroff Feb. 22, 1949 FOREIGN PATENTS 193,390 Switzerland Dec. 16, 1937 

